From patent literature and from other technical publications it is known to utilize photoluminescence in semiconductor materials for measurement of parameters, such as temperature and pressure. The sensor in these known devices is illuminated with incident light via an optical fiber. Through this illumination, light of a wavelength different from that of the incident excitation light is generated by photoluminescence in the material. This emitted luminescent light can be analyzed in different ways, for example with regard to total intensity, spectral distribution or with respect to its dynamic properties. Irrespective of which of the above-mentioned methods is utilized it is desirable that the sensor material has a high external efficiency. A higher signal level can then be obtained in the detector, and thus a higher signal/noise ratio is obtained. If a semiconductor material is utilized in the sensor so that band-band excitation takes place, this will occur near the surface of the sensor, whereby the efficiency of the sensor is often limited by recombination of excited charge carriers via energy states near the surface of the crystal. This creates problems when it is desired to manufacture sensors with high efficiency.
For a material such as GaAs, it has been reported that the luminescence spectrum is changed by heat treatment. This change is due to the formation of new recombination paths caused by a modification of the material near its surface. In measuring devices in which spectral analysis is carried out, this phenomenon may have an effect on the long-term stability of the measuring device.
In those cases where the measuring system utilizes some form of analysis of dynamic properties of the luminescent light, it is desirable for the sensor material to exhibit an exponential curve during increase and decay of the luminescent light. If this is the case, the measuring system can be simply designed so that the relation between the quantity to be measured and the measuring signal becomes independent of the excitation intensity, to compensate for any instability in the fiber optics and for any drift in a light-emitting diode used for the incident excitation light.
In the majority of Group II-VI semiconductor materials with a high luminescence intensity, the technical literature indicates a non-exponential time dependence, which is usually caused by so-called traps in the semiconductor material.